1. Field of the Invention
This invention relates to an eletrolytic manganese dioxide having particular properties, a process for preparing the same, and a manganese dry cell comprising a cathode active material comprised of a mixture of said electrolytic manganese dioxide with a conductive acetylene black, especially a conductive acetylene black having a BET specific surface area of 70 to 250 m.sup.2 /g, and an electrolyte composed mainly of zinc chloride and/or ammonium chloride.
2. Description of the Prior Art
A manganese dry cell comprising an electrolytic manganese dioxide as a cathode active material, a zinc alloy as an anode active material, and an aqueous solution, as an electrolyte, composed mainly of zinc chloride and/or ammonium chloride is well known in the art.
The electrolytic manganese dioxide used in the cathode of this manganese dry cell has hitherto been prepared, for example, by practicing the steps of electrolysis, then washing with water or hot water, and neutralization. A manganese dry cell using the above electrolytic manganese dioxide as the cathode has a problem that, during storage, the electrolytic manganese dioxide is reacted with a conductive acetylene black to evolve carbon dioxide gas, increasing the internal resistance during discharge, which causes the properties to deteriorate with prolonging the storage period. This tendency is more significant under high drain conditions required, in recent years, of dry cells, making it urgently necessary to solve this problem.
Further, in recent years, in order to improve high drain characteristics of manganese dry cells, an attempt has been made to use a conductive acetylene black having a high specific surface area to improve the ability of the electrolytic manganese dioxide to absorb and hold the electrolyte necessary for the discharge reaction. The conductive acetylene black having such a high specific surface area, however, unfavorably has high reactivity with the electrolytic manganese dioxide.
On the other hand, a conductive acetylene black having a low reactivity with the electrolytic manganese dioxide is unsatisfactory in the capability of holding the electrolyte, resulting in deteriorated high drain characteristics.
In order to overcome this problem, the electrolytic manganese dioxide can be heated in air to lower the reactivity. This, however, reduces the amount of adhesive moisture which is very important for discharge characteristics of manganese dry cells. In particular, heating at 100.degree. C. or above results in loss of bound water as well, posing a problem that the initial discharge characteristics per se of the dry cells are remarkably deteriorated.
Storage of the electrolytic manganese dioxide for a very long period of time is another means to prevent the reaction between the electrolytic manganese dioxide with the conductive acetylene black. However, it is difficult to produce such electrolytic manganese dioxide on a commercial scale.